/**
 * Provides easing functionality
 */
var Easing = {
	Linear: {
		None: function (k) {
			return k;
		},
		In: function (k) {
			return k;
		},
		Out: function (k) {
			return k;
		},
		InOut: function (k) {
			return k;
		}
	},
	Quadratic: {
		In: function (k) {
			return k * k;
		},
		Out: function (k) {
			return k * (2 - k);
		},
		InOut: function (k) {
			if ((k *= 2) < 1) {
				return 0.5 * k * k;
			}
			return - 0.5 * (--k * (k - 2) - 1);
		}
	},
	Cubic: {
		In: function (k) {
			return k * k * k;
		},
		Out: function (k) {
			return --k * k * k + 1;
		},
		InOut: function (k) {
			if ((k *= 2) < 1) {
				return 0.5 * k * k * k;
			}
			return 0.5 * ((k -= 2) * k * k + 2);
		}
	},
	Quartic: {
		In: function (k) {
			return k * k * k * k;
		},
		Out: function (k) {
			return 1 - (--k * k * k * k);
		},
		InOut: function (k) {
			if ((k *= 2) < 1) {
				return 0.5 * k * k * k * k;
			}
			return - 0.5 * ((k -= 2) * k * k * k - 2);
		}
	},
	Quintic: {
		In: function (k) {
			return k * k * k * k * k;
		},
		Out: function (k) {
			return --k * k * k * k * k + 1;
		},
		InOut: function (k) {
			if ((k *= 2) < 1) {
				return 0.5 * k * k * k * k * k;
			}
			return 0.5 * ((k -= 2) * k * k * k * k + 2);
		}
	},
	Sinusoidal: {
		In: function (k) {
			return 1 - Math.cos(k * Math.PI / 2);
		},
		Out: function (k) {
			return Math.sin(k * Math.PI / 2);
		},
		InOut: function (k) {
			return 0.5 * (1 - Math.cos(Math.PI * k));
		}
	},
	Exponential: {
		In: function (k) {
			return k === 0 ? 0 : Math.pow(1024, k - 1);
		},
		Out: function (k) {
			return k === 1 ? 1 : 1 - Math.pow(2, - 10 * k);
		},
		InOut: function (k) {
			if (k === 0) {
				return 0;
			}
			if (k === 1) {
				return 1;
			}
			if ((k *= 2) < 1) {
				return 0.5 * Math.pow(1024, k - 1);
			}
			return 0.5 * (- Math.pow(2, - 10 * (k - 1)) + 2);
		}
	},
	Circular: {
		In: function (k) {
			return 1 - Math.sqrt(1 - k * k);
		},
		Out: function (k) {
			return Math.sqrt(1 - (--k * k));
		},
		InOut: function (k) {
			if ((k *= 2) < 1) {
				return - 0.5 * (Math.sqrt(1 - k * k) - 1);
			}
			return 0.5 * (Math.sqrt(1 - (k -= 2) * k) + 1);
		}
	},
	Elastic: {
		In: function (k) {
			var s;
			var a = 0.1;
			var p = 0.4;

			if (k === 0) {
				return 0;
			}

			if (k === 1) {
				return 1;
			}

			if (!a || a < 1) {
				a = 1;
				s = p / 4;
			} else {
				s = p * Math.asin(1 / a) / (2 * Math.PI);
			}

			return - (a * Math.pow(2, 10 * (k -= 1)) * Math.sin((k - s) * (2 * Math.PI) / p));
		},
		Out: function (k) {
			var s;
			var a = 0.1;
			var p = 0.4;

			if (k === 0) {
				return 0;
			}

			if (k === 1) {
				return 1;
			}

			if (!a || a < 1) {
				a = 1;
				s = p / 4;
			} else {
				s = p * Math.asin(1 / a) / (2 * Math.PI);
			}

			return (a * Math.pow(2, - 10 * k) * Math.sin((k - s) * (2 * Math.PI) / p) + 1);
		},
		InOut: function (k) {
			var s;
			var a = 0.1;
			var p = 0.4;

			if (k === 0) {
				return 0;
			}

			if (k === 1) {
				return 1;
			}

			if (!a || a < 1) {
				a = 1;
				s = p / 4;
			} else {
				s = p * Math.asin(1 / a) / (2 * Math.PI);
			}

			if ((k *= 2) < 1) {
				return - 0.5 * (a * Math.pow(2, 10 * (k -= 1)) * Math.sin((k - s) * (2 * Math.PI) / p));
			}

			return a * Math.pow(2, -10 * (k -= 1)) * Math.sin((k - s) * (2 * Math.PI) / p) * 0.5 + 1;
		}
	},
	Back: {
		In: function (k) {
			var s = 1.70158;
			return k * k * ((s + 1) * k - s);
		},
		Out: function (k) {
			var s = 1.70158;
			return --k * k * ((s + 1) * k + s) + 1;
		},
		InOut: function (k) {
			var s = 1.70158 * 1.525;
			if ((k *= 2) < 1) {
				return 0.5 * (k * k * ((s + 1) * k - s));
			}
			return 0.5 * ((k -= 2) * k * ((s + 1) * k + s) + 2);
		}
	},
	Bounce: {
		In: function (k) {
			return 1 - Easing.Bounce.Out(1 - k);
		},
		Out: function (k) {
			if (k < (1 / 2.75)) {
				return 7.5625 * k * k;
			} else if (k < (2 / 2.75)) {
				return 7.5625 * (k -= (1.5 / 2.75)) * k + 0.75;
			} else if (k < (2.5 / 2.75)) {
				return 7.5625 * (k -= (2.25 / 2.75)) * k + 0.9375;
			} else {
				return 7.5625 * (k -= (2.625 / 2.75)) * k + 0.984375;
			}
		},
		InOut: function (k) {
			if (k < 0.5) {
				return Easing.Bounce.In(k * 2) * 0.5;
			}
			return Easing.Bounce.Out(k * 2 - 1) * 0.5 + 0.5;
		}
	}
};

module.exports = Easing;
